chance 
(chăns)
(chăns)n.
1.
a. The unknown and unpredictable element in happenings that seems to have no assignable cause.
b. A force assumed to cause events that cannot be foreseen or controlled; luck: Chance will determine the outcome.
2. often chances The likelihood of something happening; possibility or probability: Chances are good that you will win. Is there any chance of rain?
3. An accidental or unpredictable event: "He sprang to his feet and turned to run. At the same moment by a lucky chance the moon broke through the clouds" (Arthur Conan Doyle).
4. A favorable set of circumstances; an opportunity: a chance to escape.
5. A risk or hazard; a gamble: took a chance that the ice would hold me.
6. Games A raffle or lottery ticket.
7. Baseball An opportunity to make a putout or an assist that counts as an error if unsuccessful.
adj.
Caused by or ascribable to chance; unexpected, random, or casual: a chance encounter; a chance result.
tr.v. chanced, chanc·ing, chanc·es
Phrasal Verb: 1. To take the risk or hazard of: We thought we could jump over the puddle, but we were not willing to chance it.
2. To have the fortune (to be or do something); happen: "My eye chanced to fall on the wizened houseplant on the windowsill" (Elisabeth Brink).
3. Used with the impersonal subject it and a following clause or infinitive to indicate the occurrence of a usually unexpected or chance event: "Now it chanced that this car-line was owned by gentlemen who were trying to make money" (Upton Sinclair).
chance on (or upon)
Idioms: To find or meet accidentally; happen upon: While in Paris we chanced on two old friends.
by chance
1. Without plan; accidentally: They met by chance on a plane.
2. Possibly; perchance: Is he, by chance, her brother?
on the off chance
In the slight hope or possibility.
[Middle English, unexpected event, from Old French, from Vulgar Latin *cadentia, from Latin cadēns, cadent-, present participle of cadere, to fall, befall; see kad- in the Appendix of Indo-European roots.]
Synonyms: chance, random, casual, haphazard, desultory
These adjectives apply to what is determined not by deliberation but by happenstance. Chance stresses lack of intention or premeditation: a chance meeting with a friend.
Random implies the absence of a specific pattern or objective: at the mercy of random events.
Casual stresses the indiscriminate or unpredictable nature of chance events: "the casual mutation of one of your liver cells from normal to cancerous" (John Barth).
Haphazard implies a carelessness or lack of control: "If unmarried significant others are invited to participate in the family support groups at all, it tends to be on a haphazard, informal basis" (Kristin Henderson).
Desultory denotes a sporadic or aimless sequence of events: "I lay on a shared cot listening to desultory gunfire" (Jan Clausen). See Also Synonyms at happen, opportunity.
These adjectives apply to what is determined not by deliberation but by happenstance. Chance stresses lack of intention or premeditation: a chance meeting with a friend.
Random implies the absence of a specific pattern or objective: at the mercy of random events.
Casual stresses the indiscriminate or unpredictable nature of chance events: "the casual mutation of one of your liver cells from normal to cancerous" (John Barth).
Haphazard implies a carelessness or lack of control: "If unmarried significant others are invited to participate in the family support groups at all, it tends to be on a haphazard, informal basis" (Kristin Henderson).
Desultory denotes a sporadic or aimless sequence of events: "I lay on a shared cot listening to desultory gunfire" (Jan Clausen). See Also Synonyms at happen, opportunity.